Road to Merton: Feature for Energy in Buildings & Industry

To Merton and beyond: can renewable technologies and concrete thermal mass systems combine to deliver greater carbon savings in buildings? By Geoff Russell-Smith, general manager, TermoDeck.

As the annual venue of the Wimbledon Lawn Tennis Championships, the London Borough of Merton is typically associated with blistering cross-court shots and strawberries and cream. Now, thanks to Merton Borough Council’s groundbreaking drive to cut carbon emissions in the built environment, the Borough could also be a flagship destination for all those wanting to view the best in low-carbon construction.

This status is well earned. In 2003, Merton Borough Council became the first local authority in the UK to use its planning powers to dictate that non-residential developments over 1,000 sq metres utilise onsite renewable technologies to reduce annual carbon emissions by 10 per cent across all new developments.

New planning powers

Today, Merton no longer stands alone as a solitary beacon of best practice. Around 75 local authorities from Croydon to North Devon have taken proactive steps to follow this approach, which has been dubbed the ‘Merton Rule’. This figure is now set to rise dramatically as the recent Local Government White Paper indicated that all local authorities must in future become more accountable for meeting individual carbon targets and cutting emissions in the communities that they serve.

The message for all practitioners involved in the planning, design and energy management of non-residential buildings is clear. Further changes to planning policy will dictate that renewable technologies like biomass boilers, ground source heat pumps and solar panels become widespread and are no longer just confined to one-off, ‘best practice’ developments.

Building on renewables

This is good news. However, I believe that the key to building, and successfully managing, low carbon commercial buildings is the integration of renewable energy sources into thermally efficient new builds. In the London Renewables document, a preferred hierarchy states that renewables should be considered once the potential to maximise a building’s energy efficiency and Combined Heat & Power (CHP) have been fully explored.

This makes complete sense. If you are looking for 10 per cent of the building’s energy usage to come from renewables, then minimising the 100 per cent energy figure makes achieving the 10 per cent renewables content easier and cheaper. Not only is this important to realising further carbon savings, but an inefficient building can also incur significantly greater capital plant costs and operational life-time costs.

High cost of inefficiency

To date, the selection and installation of renewable technologies only becomes cost-effective when considered over the whole life cycle of a building. For example, a thermally inefficient building using ground photovoltaic (PV) solar panels requires a higher renewables input, resulting in the need for larger and more expensive solar arrays. So carefully selecting, sizing and costing the renewable element on an energy-efficient building decreases capital cost involved and improves paybacks calculations.

Achieving thermally efficient buildings

One approach to achieving thermally efficient buildings is to incorporate high thermal mass into the initial design, as heavyweight structures deliver stable, comfortable temperatures to internal spaces. Because a concrete-cored building has a very high thermal mass, it can ensure there is a resistance to the flow of heat or conversely, ‘coolth’, through the building’s dense material. Once dense materials like concrete reach their maximum internal temperature, the slow release of heat helps maintain comfortable room temperatures for a period of time after the initial heat input has been made.

Controlled comfort

Importantly, in high thermal mass structures, external room temperature variations are not reproduced inside the building, because the maximum heat level reached during the day is delayed by the thermal mass of the building until counterbalanced by the cool of the night. This ‘thermal lag’ greatly reduces the need for further energy consumption.

The passive use of thermal mass, as described in conjunction with high levels of insulation, is a solid start in good building design practice. To achieve the more rigorous energy performances demanded by new legislation, a more active approach is required, such as the use of the TermoDeck system.

TermoDeck exploits the high thermal mass of structural, hollowcore concrete slabs to control internal temperatures and distribute warmed or cooled fresh air through a building. The supply air passes through the hollowcore at low velocities allowing prolonged contact between the air and the slabs. In turn, this enables the concrete to behave as passive heat exchange elements that release heat to, or absorb heat from, the air in the slabs.

In a well-insulated, airtight concrete building, which has good heat recovery, TermoDeck can successfully utilise the clear thermal mass benefits to produce an efficient environmental system. As a result, the system can replace the need for potentially inefficient refrigerant-based air conditioning systems.

The TermoDeck system delivers 100 per cent fresh air with a reliability that natural ventilation cannot offer, ensuring an indoor atmosphere that is quiet, fresh and keeps occupants alert - whether they be employees, students or pupils!

A combined approach

TermoDeck also has the vast potential to be used in buildings that utilise renewable technologies and can work in tandem to help deliver greater thermal efficiency, whilst also contributing to reduced carbon emission targets.

Currently being built, the new Phase 3 building at Malvern Hills Science Park, Worcestershire, is one the first buildings in the UK to combine both TermoDeck and ground source heat pumps. Boreholes have been drilled to enable four 90Kw ground source heat pumps to add heat or cooling capacity into the building. Couch Perry Wilkes, the building services consultants on the project, saw ground source heat pumps the ideal renewable option to reduce the already low energy profile of the building.

To Merton and beyond <br>Already, a small number of local authorities are seeking carbon reduction targets beyond the 10 per cent prescribed by the Merton Rule. It is clear that many authorities in the UK will be following the lead set by Merton. It is also apparent that the 10 per cent renewable factor will increase to 20 per cent and beyond. This will create new challenges for building design. High thermal mass systems like TermoDeck are one such way in which these challenging targets can be met, by achieving savings on carbon emissions and reduced running costs, whilst also providing comfortable internal environments for new commercial buildings.

See more on Tarmac TermoDeck.

Date: 23 January 2009

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Fact 14

Low embodied energy…

Like all concrete, during its lifetime Precast concrete will effectively re-absorb the equivalent amount of energy (carbon dioxide) that was used to create it I the first place! What’s more, using Precast doesn’t require any re-mineralisation (the process of rejuvenating barren soils after they have been intensely forested).

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